Campbell CR800 Spécifications télécharger pdf (Page 237)

Section 8. Processing and Math Instructions

The TimeIntoInterval instruction has the following parts:

TintoInt The TintoInt, or time into interval, argument allows the programmer

to define an offset from the Interval at which the TimeIntoInterval statement

will be evaluated true. For example, if the Interval is set at 60 minutes, and

TintoInt is set to 5, TimeIntoInterval will be True at 5 minutes into the hour,

every hour, based on the datalogger's real-time clock. If the TintoInt is set to

0, the TimeIntoInterval statement is True at the top of the hour.

Interval The Interval is how frequently the TimeIntoInterval statement will be

evaluated True, based on the datalogger's real-time clock.

Units The Units argument is used to specify the units on which the TintoInt

and Interval arguments will be based. The options are microseconds,

milliseconds, seconds, minutes, hours, or days.

Notes:

TimeIntoInterval must be placed within a scan to function.

This instruction is also known as IfTime. Either keyword can be used within

the program.

VaporPressure (Dest, Temp, RH)

The VaporPressure instruction calculates the ambient vapor pressure (Vp) from

previously measured values for air temperature and RH. The instruction first

calculates saturation vapor pressure from air temperature using Lowe’s

equation (see SatVP). Vapor pressure is then calculated by multiplying by the

fractional RH:

Vp = SatVp x RH/100

WetDryBulb (Dest, Temp, WetTemp, Pressure)

WetDryBulb calculates vapor pressure in kilopascals from the wet and dry-

bulb temperatures in °C. This algorithm type is used by the National Weather

Service:

Vp = Svpwet - A (1 + B∗Tw)(Ta - Tw) P

Vp = ambient vapor pressure in kilopascals

Svpwet = saturation vapor pressure at the wet-bulb temperature in kilopascals

Tw = wet-bulb temperature, °C

Ta = ambient air temperature, °C

P = air pressure in kilopascals

A = 0.000660

B = 0.00115

Although the algorithm requires an air pressure entry, the daily fluctuations are

small enough that for most applications a fixed entry of the standard pressure

at the site elevation will suffice. If a pressure sensor is employed, the current

pressure can be used.

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Campbell CR800 Spécifications Page 237